This invention relates generally to carbon-based nanotube probes for microscopy devices, and particularly to superconducting nano-channels for guiding and manipulating electron beams or other charged particles.
Carbon-based nanotube probes for microscopy devices, and superconducting nano-channels for guiding and manipulating electron beams or other charged particles in particular.
Many analytical devices, such as electron microscopes, are used to image the topography and surface properties of a substrate. These devices utilize a focused beam of electrons to illuminate a substrate. Sources of these electron beams are often contained in the tips of the analytical device.
Electron point sources, which may be utilized in these analytical devices, are well known. These electron point sources, often on the order of the atomic scale and adapted to provide field emission of coherent electron beams, have been described in, e.g., xe2x80x9cCoherent point source electron beamsxe2x80x9d, Hans-Werner Fink, Werner Stocker, and Heinz Schmid, Journal of Vacuum Science and Technology B, Volume 8, Number 6, Nov/Dec 1990, pp. 1323-1324, in xe2x80x9cUnraveling nanotubes: field emission from an atomic wire,xe2x80x9d A. G. Rinzler, J. H. Hafner, P. Nikolaev, L. Lou, S. G. Kim, D. Tomanek, P. Nordlander, D. T. Colbert and R. E. Smalley, Science, 269, pp. 1550-1553 (1995), and in xe2x80x9cCarbon nanotubes are coherent electron sourcesxe2x80x9d, Heinz Schmid, Hans-Werner Fink, Applied Physics Letters, Volume 70, Number 20, 19 May 1997, pp. 2679-2680. The first reference discloses a tungsten tip terminated with an atomically perfect pyramid of tungsten atoms as the electron emitter. The second and third references disclose a carbon nanotube as the electron emitter.
By way of further illustration, U.S. Pat. No. 5,654,548 (xe2x80x9cSource for intense coherent electron pulsesxe2x80x9d) discloses how such sources can be used for one type of electron microscopy. The entire disclosure of this United States patents is hereby incorporated by reference into this specification.
Electron beams have been used in constructing microscopes. For example, U.S. Pat. No. 6,005,247 (Electron beam microscope using electron beam patterns) discloses xe2x80x9cAn electron beam microscope includes an electron beam pattern source, a vacuum enclosure, electron optics, a detector and a processor.xe2x80x9d U.S. Pat. No. 6,043,491 (Scanning electron microscope) discloses xe2x80x9cA scanning electron microscope in the present invention, by employing a retarding method and suppressing interferences between an electron beam and secondary electrons or back scattered electrons, makes it possible to obtain a clearer SEM image with a higher resolution.xe2x80x9d The entire disclosure of each of these United States patents is hereby incorporated by reference into this specification.
Field emitted electron beams are also useful in many types of vacuum microelectronic devices, as described in xe2x80x9cVacuum Microelectronics,xe2x80x9d edited by Wei Zhu, (John Wiley and Sons, New York, 2001).
Fabrication of specialized tips used in scanning electron microscopes and atomic force microscopes is well known to those skilled in the arts. For example, U.S. Pat. No. 6,020,677 (Carbon cone and carbon whisker field emitters) discloses xe2x80x9cCarbon cone and carbon whisker field emitters are disclosed. These field emitters find particular usefulness in field emitter cathodes and display panels utilizing said cathodes.xe2x80x9d U.S. Pat. No. 5,393,647 (Method of making superhard tips for micro-probe microscopy and field emission) discloses xe2x80x9cForming micro-probe tips for an atomic force microscope, a scanning tunneling microscope, a beam electron emission microscope, or for field emission, by first thinning a tip of a first material, such as silicon.xe2x80x9d The entire disclosure of each of these United States patents is hereby incorporated by reference into this specification.
The prior art sources of atomic point source electron beam emitters typically must be operated at very low pressures, on the order of about 10-8 to 10-10 Torr, to protect them from disruptive contamination, chemical degradation, or destructive ion bombardment by residual gas ions. This often requires the use of complicated, expensive, and cumbersome equipment.
Carbon-based nanotubes may be configured as superconducting nano-channels. Nanotubes are resilient and have nanometer-scale, sharp tips. As such, they are useful for making micro-probe tips of microscopy devices, e.g., scanning tunneling microscope and atomic force microscope. The dimensions of carbon-based nanotubes, ideally having a single atom at the tip apex, but typically being 3 to 10 atoms in diameter at the tip, allows the tip to be positioned close enough to a conducting substrate so that a tunneling current flows between the tip and the substrate under an applied bias voltage. This tunneling current is similar to the tunneling of electrons across a barrier as described by the Josephson tunneling effect, which is obtained from a system comprising two layers of superconductive material separated by a barrier. The two layers are either connected by a very narrow conductive bridge, or are separated by a layer of nonconductive material. When this system is under superconducting conditions (low temperature), a tunneling effect takes place, in which a superconducting current or super current flows across the barrier between the superconductive layers.
In the case of carbon-based superconducting nanotubes, the barrier is the repulsive force of the Meissner effect between the superconducting carbon-based nanotube and substrate. The Meissner effect is the ability of a material in a superconducting state to expel all magnetic fields therefrom (i.e., such a superconductor is perfectly diamagnetic and exhibits a permeability of zero). Reference may be had to xe2x80x9cThe Further Inventions of Daedalusxe2x80x9d, by David E. H. Jones, Oxford Press, 1999. In the section relating to xe2x80x9cElectric Gas Light on Tapxe2x80x9d (pages 174-175) the author describes methods for exploiting the Meissner effect of evacuated superconducting tubes for purposes of residential electric beam-based power distribution. Further reference may be had, e.g., to U.S. Pat. No. 4,975,669 (Magnetic bottle employing Meissner effect). The entire disclosure of this United States patent is hereby incorporated by reference into this specification. Atomic force microscopes, which rely on the repulsive force generated by the overlap of the electron cloud at the tip""s surface with electron clouds of surface atoms within the substrate, negate the need of conducting substrates to obtain the same effect.
As used herein, the term xe2x80x9cnanotubexe2x80x9d refers to a hollow structure having a diameter of from about 0.3 to about 10 nanometers, and a, length of from about 3 to about 10,000 nanometers. In general, such nanotubes have aspect ratios of at least about 1:10 to about 1:1000. Carbon-based nanotubes are hollow structures composed between 95-to100% of carbon atoms. In general, the most commonly studied forms of nanotubes have physical properties such that they conduct electricity better than copper. Typically, carbon nanotubes have tensile strength 100 times that of steel. Carbon nanotubes become superconductors at very low temperatures. Nanotubes may be fabricated from materials other than carbon, e.g., Tungsten disulphide, Molybdenum disulphide, and Boron nitride. Carbon nanotubes may be capped with metallic cores. Carbon nanotubes can be doped with other elements, e.g. metals.
Carbon-based nanotubes may be either single-walled nanotubes (SWNT) or multi-walled nanotubes (MWNT). A MWNT includes several nanotubes each having a different diameter. Thus, the smallest diameter nanotube is encapsulated by a larger diameter nanotube, which in turn, is encapsulated by another larger diameter nanotube. Carbon-based nanotubes are used to form superconducting nanochannels for steering and channeling very fine electron beams or other charged particles. In order to preserve near perfect vacuum and ultra-clean conditions, the outlet ends of the superconducting nanochannels are sealed with electron transparent nano-membranes.
Fabrication of specialized tips comprising carbon-based nanotubes and its use in scanning electron microscopes and atomic force microscopes is well known to those skilled in the arts. For example, U.S. Pat. No. 6,020,677 (Carbon cone and carbon whisker field emitters) discloses xe2x80x9cCarbon cone and carbon whisker field emitters. These field emitters find particular usefulness in field emitter cathodes and display panels utilizing said cathodes.xe2x80x9d U.S. Pat. No. 5,393,647 (Method of making super hard tips for micro-probe microscopy and field emission) discloses xe2x80x9cForming micro-probe tips for an atomic force microscope, a scanning tunneling microscope, a beam electron emission microscope, or for field emission, by first thinning a tip of a first material, such as silicon.xe2x80x9d The entire disclosure of each of these United States patents is hereby incorporated by reference into this specification.
Electron transparent nano-membranes are well known to those skilled in the art. Reference may be had, e.g., to U.S. Pat. Nos. 6,300,631 (Method of thinning an electron transparent thin film membrane on a TEM grid using a focused ion beam), 6,194,720 (Preparation of transmission electron microscope samples), 6,188,068, 6,140,652, 6,100,639, 6,060,839, 5,986,264, 5,940,678 (Electronic transparent samples), 5,633,502, 4,680,467, 3,780,334 (Vacuum tube for generating a wide beam of fast electrons), and the like. The entire disclosure of each of these United States patents is hereby incorporated by reference into this specification.
The prior art sources of carbon-based nanotube applications for microscopy devices typically consist of attaching a carbon-based nanotube to the tip of a microscopy probe. The prior art, however, does not include microscopy probes incorporating superconducting nano-channels comprising carbon-based nanotubes, which are capable of guiding and manipulating charged particle beams for microscopy applications. In the remainder of this specification reference will be made to the use of single walled superconducting carbon nanotubes. However, it is to be understood that multi-walled superconducting carbon nanotubes may be utilized as well, as may be any other essentially atomically perfect nanotube structure, which, if not naturally superconducting, may be optionally externally coated with a thin film of superconducting material.
It is an object of this invention to provide superconducting nanochannels structures configured for guiding and manipulating electron beams or other charged particles. The superconducting nanochannels of this invention comprise carbon-based nanotubes, and may be used to fabricate nanometer scale tips for a microscopy probe.
In accordance with the present invention, there is provided a device for guiding a charged particle beam comprising a superconducting nano-channel consisting essentially of a superconducting material in the form of a tube having a proximal end, a distal end, and a bend disposed between said proximal end and said distal end.
In accordance with the present invention, there is further provided a device for guiding a charged particle beam comprising a first superconducting nano-channel formed by a substrate, a first area of superconducting material coated on said substrate and having a first edge, a second area of superconducting material coated on said substrate and having a second edge, wherein said first edge of said first area of superconducting material and said second edge of second area of superconducting material are substantially parallel.
In accordance with the present invention, there is further provided a device for guiding a charged particle beam comprising a superconducting nano-channel formed by a plurality of nano-scale superconducting rods disposed around a central region.
In accordance with the present invention, there is further provided a device for guiding a charged particle beam comprising a superconducting nano-channel comprising a first split and a second split disposed parallel to the central axis of said nano-channel, said first and second splits forming a first section and a second section of said nano-channel.